handler.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
)

// a custom type that we can use for handling errors and formatting responses
type handler func(w http.ResponseWriter, r *http.Request) (interface{}, *errorHandler)

// attach the standard ServeHTTP method to our handler so the http library can call it
func (fn handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// call the actual handler
	response, err := fn(w, r)

	// check for errors
	if err != nil {
		log.Printf("ERROR: %v\n", err.Error)
		http.Error(w, fmt.Sprintf(`{"error":"%s"}`, err.Message), err.Code)
		return
	}
	if response == nil {
		log.Printf("ERROR: response from method is nil\n")
		http.Error(w, "Internal server error. Check the logs.", http.StatusInternalServerError)
		return
	}

	// turn the response into JSON
	bytes, e := json.Marshal(response)
	if e != nil {
		http.Error(w, "Error marshalling JSON", http.StatusInternalServerError)
		return
	}

	// send the response and log
	w.Header().Set("Content-Type", "application/json")

	// Allow cors
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("Access-Control-Allow-Method", "GET,PUT,POST,DELETE")
	w.Header().Set("Access-Control-Allow-Headers", "X-Requested-With")

	w.Write(bytes)
	log.Printf("%s %s %s %d", r.RemoteAddr, r.Method, r.URL, 200)
}